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  #11  
Old 12-15-2008, 10:48 AM
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ghrocketman ghrocketman is offline
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Nothing lays down a smooth a fillet as 30-min epoxy smoothed out with a rubber-gloved acetone coated finger.
The rocket has to rest horizontally and only two fillets can be performed at a time.
Second to that is 5-min epoxy, but beware the 5-min epoxy has much less structural integrity. Don't let anyone scare you off 5-min epoxy due to the lousy heat resistance. No Model Rocket or Mid-Power rocket engine burns long enough to even remotely need a heat resistant glue unless the part is in the exhaust stream or is a 29mm min-diameter "G" power bird.
Using "advanced" epoxy glues such as Aeropoxy or West System is a needlessly expensive overkill waste for anything below an average Level 2 J-powered rocket (Warp 9 H and I motors excepted, of course)
If you HAVE to use wood glue, I have found Titebond II (NOT regular Titebond or Titebond III) has the best filleting properties available in a traditional wood glue. Much fewer pin holes if layed on in say 3 thin applications.
Plain old Elmers white glue leaves smoother fillets than any Aliphatic Resin (yellow Titebond-style) Wood Glue.
The absolute WORST yellow aliphatic wood glue for making fillets is Elmers Carpenter's Wood Glue. That stuff is the absolute worst rubbish I've ever used. I'd rather use candle wax for fillets than that crapola.
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  #12  
Old 12-15-2008, 03:13 PM
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Mark II Mark II is offline
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I get more bubbles with white glue than with anything else. I can smooth it down well with my finger and have it looking really nice, and then come back a few minutes later and find bubbles emerging from underneath the fillet. Popping them doesn't totally help, because they never completely fill in afterwards. I have never been able to totally eliminate the bubbles, which is why I rarely use white glue anymore on fins, either for attaching them or filleting them.

I have used Titebond III occasionally for fillets and have had good, bubble-free results most of the time, but I have had bubbles show up in it a few times, too. I'm almost out of it now, so maybe I'll take gh's recommendation and try Titebond II next.

I mostly use 30-minute epoxy for anything 12" long or bigger. Depending on the size of the rocket, I can make the fillets big or small. I wear a nitrile glove and smooth them down with a finger dipped in 91% isopropyl alcohol from Walmart (but now that I have some denatured alcohol, I'll use that for it). Acetone just evaporates too fast and it has a much stronger smell that alcohol, and alcohol works really well on epoxy. I like to use the longer setting epoxy because it is thinner in consistency, allowing it to flow better into the joint and to self-level. I also mask off the fins (when I remember to do so! ) , which, as GIJoe mentioned, makes for a cleaner, neater fillet. You just have to be sure to pull off the tape mask as soon (within a few minutes for 30-min. epoxy) as you have smoothed the fillet down! To keep the weight down on smaller models, I go pretty thin with the epoxy, wiping most of it off with my finger, and then I keep applying thin coats like that to build up the fillet to where I want it. I never ever get bubbles with epoxy.

If I want to make big beefy fillets on big models, or if I just want to be able to sand the fillets, I mix in Sig microballoons into it, which causes the mix to resemble paste or spackle while reducing its weight. This makes it easier to slather on big, thick fillets on those rare occasions when I need them, and it keeps their weight down. Microballoons also make the cured epoxy easy to sand. With this kind of mix, it is really important to mask off the area around the fillet, because the stuff really oozes out when you smooth it, and where it goes, it tends to stay. I'm trying to remember to do the masking myself, but it isn't a fully-developed habit yet. I will sometimes use a microballoons-epoxy mix sparingly on smaller models when I want to have a sandable fillet, and also sometimes to patch bubble holes or gaps in an existing fillet, especially if they are big. (I have also used Fill 'N Finish for this.)

On smaller models, I have been increasingly using BSI Maxi-Cure CA, swiping it very quickly with my gloved finger, waiting about a minute or so, and then hitting it with a heavy spray of BSI Insta-Set accelerator. When it is allowed to cure naturally, Maxi-Cure leaves a somewhat soft, flexible, rubbery and milky-looking fillet, but if you cure it with Insta-Set it turns glass-clear, smooth and hard as a rock! The downsides with using it are that you can't mask off the area around the fillet, you have to be quick about smoothing it (and you have to have a saturated sponge sitting in a small bowl of acetone nearby to use to wipe your gloved finger off between swipes), and you have to use fresh, just-purchased and just-opened Maxi-Cure to get the best results. You also have to keep your bottle of Insta-Set in a different room from where you apply the CA, and be ready to run to the other room with your rocket to spray it with the accelerator, in order to keep the mist from coming anywhere near your open bottle of CA. And then, after wiping off the overspray, you need to leave the model in the same room as the Insta-Set while you go back and close up your CA bottle (ideally, after you have removed your smock and gloves and left them behind! ).

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  #13  
Old 12-16-2008, 09:47 PM
Bluegrass Rocket Bluegrass Rocket is offline
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Thanks for all the help guys. I am going to try some different techniques and glues. I was using Elmers Carpenters Wood Glue and I think I'm with GHRocketman, it ain't good.
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  #14  
Old 12-16-2008, 10:13 PM
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Just make sure that, whatever you use, you smooth it down after you apply it. If the project is anything smaller than high power, that means using your finger, but make sure that it doesn't have any dried glue, paint, sawdust, etc. on it first, and that you wet it right before touching the fillet. For anything other than white or yellow glue, wear nitrile gloves (latex gloves don't provide enough of a barrier, and vinyl gloves are too loose). Use water for white glue or yellow glue, alcohol (or acetone) for epoxy, and a very light amount of acetone (or else nothing at all) for CA (don't use debonder!). I'm not sure what is needed for Fix-It clay, because I've never tried it. If it is epoxy-based, then gloves and a little denatured alcohol (probably) are what you would use.

And, as Tim mentioned, you can always patch any holes with FNF or putty. Once the fillets are covered with paint, no one will be able to tell.

Mark \\.
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  #15  
Old 12-16-2008, 11:01 PM
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I've learned that to prevent bubbles in elmers... I soak the bottle in hot water, then apply while the glue is warm...
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  #16  
Old 12-17-2008, 12:57 AM
zog139 zog139 is offline
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What I want to know is how well your fillets hold up ? I've used everything mentioned here and have no clear winner for broken fins on impact. Does anyone have anything that they think really helps with preventing of "popping" fins on impact.


Jim
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  #17  
Old 12-17-2008, 07:19 AM
Peartree Peartree is offline
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Quote:
Originally Posted by Bluegrass Rocket
Thanks for all the help guys. I am going to try some different techniques and glues. I was using Elmers Carpenters Wood Glue and I think I'm with GHRocketman, it ain't good.


Quote:
Originally Posted by zog139
What I want to know is how well your fillets hold up ? I've used everything mentioned here and have no clear winner for broken fins on impact. Does anyone have anything that they think really helps with preventing of "popping" fins on impact.


Jim


Strength. That's why I said I like Carpenter's glue as a first pass. I have almost never had a problem with the glue joint popping or breaking. I've broken fins and had them separate from tube fins WITH several layers of paper, but the joints themselves have been rock solid. When smoothed out with a finger they're nice enough to get by as far as looks go and to get a pretty joint for models that I've cared more about, I follow with a layer of white glue and maybe fill any remaining voids with Fill-n-finish. I have often used carpenters glue (or white glue) to paper my fins as well. I'm sure epoxy makes a beautiful joint and I've used it in the very few MPR rockets I have built, but I just can't see adding that kind of weight to something I want to fly on A motors (or smaller). YMMV.
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  #18  
Old 12-17-2008, 07:26 AM
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Quote:
Originally Posted by zog139
What I want to know is how well your fillets hold up ? I've used everything mentioned here and have no clear winner for broken fins on impact. Does anyone have anything that they think really helps with preventing of "popping" fins on impact.


Jim

In addition to what Peartree had to say, an old method was to use glue "rivets". Using a needle or T-pin, you put holes in the BT where the root of the fin will attach. Using the double glue meathod, the glue would go into the holes and theoretically form a bulge or 'rivet' on the inside of the BT. Of course, this method only works when using larger than minimum diameter BTs. Personally, I just prefer using the double glue method. I've had fins rip the BT before breaking the glue joint just as Peartree has.....
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  #19  
Old 12-17-2008, 07:32 AM
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Sometimes something has to give on a hard landing. I usually have balsa fins break above the joint instead of having the glue joint give way, just from doing an average white or yellow glue fillet. I've come to the point that I'd rather the fin snap off than for it to rip up the body tube, so I don't usually fool with rivets anymore.

I haven't read through all the replies, so this may have been mentioned. Another thing for good joints is to sand a bit of the glassine covering away where your fin will be. That lets the glue penetrate the paper instead of sitting on top of it. Sand a wide enough strip that the fillets will also penetrate the paper. Don't sand deep, just get the shiny slick stuff off of it.
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  #20  
Old 12-17-2008, 07:57 AM
micromeister micromeister is offline
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Hard landings are more a problem of matching the recovery system to the model than whatever fin attachment method. To small a chute or streamer is going to result in damage regardless of how well we fillet the fin joints.

I do a lot of carpentry and cabinet work so I've LONG been a fan of good old elmers Yellow aliphatic carpenters wood glue. Further I've used it for model and LMR building for decades. When fins ocassionaly but rarely break, it's NEVER at the joint, alway in the fin material outside the fillets. Don't let anyone scare you away from Elmers Carpenters Glue. IF anything it's not the glue but the applicator and techniuqe that makes the difference

As several have mentioned a small bead to start using preheated (hot water bottle bath) glue works really well on even the largest fin joints. Personally I generally do a second larger bead to get the radius I'm looking for.

I also like Devcon 5 minute epoxy for fillets if your in a rush. With model over 25year old still flying with those same old 5 minute epoxy fillets I don't think it's lower heat resistance
can be considered a problem. I can't testify to other "brand" epoxies but if you'll find and use DEVCON in either it's 5 or 2-ton (15minute) formulas it won't let you down.

You don't need acetone to smooth the fillets either; Plain old rubbing alcohol does a fine job of smoothing and removing any unwanted uncured epoxy from the model and or other areas.
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